ESSEN, Germany—German Chancellor Angela Merkel called for the prohibition in some situations of the full facial veil, toughening her rhetoric toward Muslim immigrants as she sought to shore up her party’s conservative flank at its annual convention on Tuesday.

“We show our face in interpersonal communication,” Ms. Merkel told delegates of her Christian Democratic Union party to some of the strongest applause of her more than hourlong speech. “Because of this, the full veil is unacceptable for us. It should be banned wherever legally possible.”

Ms. Merkel also said that German law superseded Islamic law, or Shariah, in a nod to criticism that her policy of accepting refugees had undermined the rule of law in the country. Some 890,000 asylum seekers arrived in Germany last year, largely from Muslim countries, as Ms. Merkel refused to close the country’s borders to refugees.

Ms. Merkel’s tougher rhetoric doesn’t necessarily herald a change in policy. In September, she said that a ban on burqas would be appropriate in certain situations such as in courtrooms or the civil service, but wearing the veil was generally protected by the constitutional guarantee of freedom of religion.

The convention speech amounted to Ms. Merkel’s road map to fighting populism as her center-right party enters an election year that she said would be the most difficult since German reunification.

‘We show our face in interpersonal communication. Because of this, the full veil is unacceptable for us. It should be banned wherever legally possible.’

—German Chancellor Angela Merkel

Ms. Merkel repeated her promise that last year’s chaotic wave of migration to Germany wouldn’t repeat. The detention of a 17-year-old Afghan asylum-seeker on suspicion of raping and murdering a university student in Freiburg, and the detention of a 31-year-old Iraqi asylum-seeker for two alleged sex crimes against students in Bochum, have inflamed the immigration debate in recent days.

The Christian Democrats still hold a wide lead in the polls, and the upstart, anti-immigrant AfD has virtually no chance of entering government next year. But the party’s rise has made Christian Democrats nervous because it has attracted past supporters of Ms. Merkel who are upset by her refugee policy and could complicate her ability to form a new government next year.

The internal discord was reflected in Ms. Merkel’s less-than-unanimous reelection as party chairwoman. About 89.5% of the party delegates voted for her on Tuesday, compared to 96.7% at the previous election, in 2014.

Ms. Merkel exhorted her colleagues to avoid divisive rhetoric and defended European integration.

“In this situation in which the world has come out of joint, we must first do everything to make sure that Europe doesn’t come out of its crises even weaker than how it entered them,” Ms. Merkel said. “We must do this deeply in our own interest, since Germany will do well in the long term only when Europe also does well.”

The anti-establishment mood sweeping Europe has rattled Ms. Merkel, the European Union’s most influential politician and a staunch defender of liberal values and international institutions. The latest blow came on Sunday, when Italian voters rejected Prime Minister Matteo Renzi’s proposed constitutional changes.

Ms. Merkel said that managing the consequences of the digital revolution and globalization was one of the party’s main challenges, casting the rise of populism in the West as a by-product of those economic changes. She said financial-market regulation needed to be improved and tax loopholes for global corporations removed.

While some people benefited from the modern economy, she said, others feared losing their jobs and that things were changing too fast.

“Some blame the liberal, constitutional state for all of this and fight against its values,” Ms. Merkel said. To defend liberal society, she said, politicians had to show that “hard work will still pay off, today and in the future.”